Which while maybe not fitting a recession definition
that requires a contraction in economic output, is still
pretty disappointing when you consider that for all of its
problems, China — the world's second-largest economy — is set to
grow more than 6% this year.

(And I mean, sure, that's sort of the whole point: is China
really growing at that pace?)

Anyway, here's the case from a note Thursday out of Citi's
economics team led by Ebrahim Rahbari, Willem Buiter, and Cesar
Rojas (emphasis ours):

We believe that we are currently in a highly
precarious environment for global growth and asset markets after
2-3 years of relative calm. The most recent
deterioration in the global outlook is due to a moderate
worsening in the prospects for the advanced economies (AE), a
large increase in the uncertainty about the AE outlook (notably
for the US) and a tightening in financial conditions everywhere.
Unlike most of the previous years, the most recent worsening in
global growth prospects and global sentiment is therefore driven
by the advanced economies rather than EM.

The growing threat to the global outlook rests on poor
fundamentals, which include the pre-existing fragilities related
to the structural and cyclical slowdowns in China and its
unsustainable currency regime, broken [emerging
market] growth models, excessive leverage across many
countries and sectors, and rising regional risks (Brexit) and
geopolitical risks (including in Russia, Turkey and Syria, the
South China Sea, and North Korea).

These fundamental concerns are aggravated by a crisis of
confidence that is in part fueled by a growing worry that, should
conditions deteriorate, they may not elicit an effective policy
response. The main ‘game changers’ in our view are the emerging
belief that even the US economy is no longer bullet-proof and
that policymakers (in the US and elsewhere) may not be there to
come to the rescue of their own economies, let alone the world
economy, by propping up asset prices and aggregate demand.
It is likely, in our view, that global growth will this
year once again underperform (against long-term trends and
previous year forecasts). Citi's latest forecasts are for global
growth of 2.5% in 2016 (based on market exchange rates and
official statistics) and around 2.2% (adjusted for probable
Chinese mismeasurement). But in our view, the risk of a global
growth recession (growth below 2%) is high and
rising.

So that's basically the whole laundry list of reasons to be
worried about the global economy.

And what stands out to us is Citi's contention that even a minor
issue in the US economy could sink the whole thing.

Citi again (and again, our emphasis):

A material slowdown in the US, even short of a
recession, would still be a major headwind for the world economy:
at this point, it could make a global recession according to our
definition almost unavoidable. The damage to global
growth conditions would come from three sources: deteriorating
financial conditions globally, weaker demand from the US and
weakening (consumer and business) sentiment more broadly (through
contagion).

And while economic growth in the US certainly slowed into
the end of 2015, news from the economy in 2016 has been less bad,
if still mixed.